Known in the art is that drilling mud represents a heterogeneous liquid system inevitably containing colloidal solid phase particles. The present of these particles in drilling mud determines a number of rheological properties of drilling mud which are important from the viewpoint of well drilling quality. Therefore, the process for preparing drilling mud is essentially the process for preparing clayey slurries with the content of colloidal solid phase particles at a level at which necessary rheological properties of drilling mud are obtained. The degree of dispersion or comminution of clayey solid phase particles determine the quality of drilling mud being prepared. Reduction of the total quantity of solid phase in drilling mud with the same rheological properties of drilling mud contributes to an increase in the mechanical speed of drilling. This requires an improved degree of dispersion.
Drilling mud is prepared from high-grade dry mud, and expensive chemical reagents are added thereto for controlling and stabilizing pre-set properties of drilling mud. After the drilling is over, all drilling mud is disposed into a pile since its transportation to another drilling site is too expensive owing to high transport cost as drilling mud consists at 85-90% of water. A problem, therefore, arises to separate the most valuable fraction of drilling mud--finest colloidal fraction--which constitutes the basis of the structure of drilling mud, the more so as it is rich in chemical reagents added to drilling mud.
At present drilling mud is only cleaned during drilling. There are various apparatus for cleaning drilling mud during drilling.
Such known apparatus as vibratory screen, hydrocyclones and centrifugal apparatus separate coarse lumps of drillings from drilling mud, whereas finest colloidal particles remain thus impairing the properties of drilling mud. Thus a portion of drilling mud is to be disposed, the remaining portion is diluted with water and treated with chemical reagents for maintaining desired rheological parameters of drilling mud which are important for well drilling. After the drilling is over, the drilling mud is generally disposed.
It will be apparent that separation of colloidal particles of solid phase from drilling mud is of a substantial importance for the economical performance of well drilling.
Known in the art is an apparatus for separating stable colloidal clayey phase from drilling mud, wherein drilling mud leaving the well and containing drillings is preliminarily diluted with water, and coarse drillings are separated therefrom. Fine non-charged drillings and negatively charged colloidal clayey particles are present in such diluted and cleaned drilling mud. Then negatively charged clayey particles are separated from the drilling mud by depositing them on a rotary anode, with subsequent removal by means of a scraper. The deposited negatively charged clayey particles entrain with them a portion of non-charged particles which are also deposited on the rotary anode (cf. Czechoslovakian Pat. No. 109992, cl. 5a 31/20, issued on Feb. 12, 1964).
The above-described apparatus can only treat a portion of drilling mud, whereas the remaining and much greater portion thereof is fed back to the well without treatment.
Separation of solid phase particles only from a portion of drilling mud and the two-stage character of the process: first, separation of coarse particles, and then separation of finer particles, make the process complicated and expensive.
Known in the art is an apparatus for electrokinetically separating drilling mud into liquid and solid phases, wherein a casing has an inlet for drilling mud and outlets for separated phases of drilling mud and accommodates electrodes which are connected to terminals of a d-c source.
The electrode connected to the positive terminal of the d-c source comprises a chamber having a perforated wall which is connected to a closed circuit for a circulation of an electrically conducting liquid. The casing comprises the other electrode and is connected to the negative terminal of the d-c source. In operation circulating through the chamber is enriched with solid phase, and drilling mud which is within the casing and around the chamber is depleted therefrom. After several cycles of pumping of the electrically conducting liquid through the chamber the process of cleaning of the drilling mud is completed.
After that the electrically conducting liquid enriched with solid phase is drained and replaced by fresh liquid. New batch of drilling mud is poured in the casing of the apparatus, and the cleaning process continues (cf., the USSR Inventor's Certificate No. 662688, cl. E 21 B 21/00, 1978).
The need for circulating the electrically conducting liquid limits the amount of solid phase taken in thereby.